To characterize physicochemically, the uterine receptor for oxytocin in the 20,000 x g particulate fraction of pig uterus, isolated myometrial cells from pig and rat uterus, and purified subcellular fractions obtained therefrom. To study the biochemical events resulting from oxytocin-receptor interaction and factors regulating these events in isolated uterine cells and subcellular fractions. To correlate the biochemical events with the binding of oxytocin to its receptor. To determine by kinetic parameters the steps involved in receptor activation. To construct a plausible molecular scheme for the manner in which oxytocin elicits contraction of uterine smooth muscle.